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Elagolix: A new treatment for pelvic pain caused by endometriosis

Posted on November 29, 2018

Two doses of elagolix are now FDA approved for treatment of pelvic pain caused by endometriosis. These two doses allow clinicians to opt for gentle (150 mg once daily) or strong (200 mg twice daily) suppression of estradiol to manage pelvic pain, as well as the associated effects of low estradiol levels.

Endometriosis is the presence of tissue resembling endometrial glands and stroma outside of the uterine cavity. Women with endometriosis often present for medical care with at least 1 of 3 problems: pelvic pain, infertility, and/or an adnexal mass due to endometriosis.

Many clinical observations demonstrate that endometriosis lesions require estrogen to grow and maintain their viability, including that:

Endometriosis is uncommon before puberty or after menopause.

Surgical removal of both ovaries results in regression of endometriosis lesions.

Since endometriosis lesions require estrogen to maintain their viability, suppressing estradiol is a logical approach to hormonal treatment of the disease.

The estradiol concentration that causes endometriosis lesions to grow or regress varies among women, but a concentration less than 20 pg/mL usually causes lesions to regress, and a concentration greater than 60 pg/mL usually supports lesion growth and maintains lesion viability.2 Although an estradiol concentration below 20 pg/mL may cause lesions to regress, it also is associated with moderate to severe hot flashes and accelerated bone loss. These adverse effects limit the use of strong suppression of estrogen as a long-term treatment strategy. The estrogen threshold hypothesis posits that gently suppressing estradiol to a concentration between 20 and 45 pg/mL may simultaneously cause endometriosis lesions to regress, resulting in reduced pelvic pain, minimal bone loss, and few hot flashes.2

Building on the estrogen threshold hypothesis, clinicians have two options for treatment of pelvic pain caused by endometriosis:

strong suppression of estradiol to a concentration below 20 pg/mL

gentle suppression of estradiol to a concentration in the range of 20 to 45 pg/mL

Strong suppression of estradiol to levels below 20 pg/mL will reliably induce amenorrhea and cause regression of endometriosis lesions, thereby reducing pelvic pain. Strong suppression of estradiol also will cause moderate to severe hot flashes and accelerated bone loss in many women. By contrast, gentle suppression of circulating estradiol to a concentration in the range of 20 to 45 pg/mL may result in amenorrhea or oligomenorrhea, suppression of the growth of endometriosis lesions, a modest reduction in pelvic pain, mild hot flashes, and minimal bone loss.

Recently, the US Food and Drug Administration (FDA) approved elagolix, an oral GnRH antagonist, for treatment of endometriosis.3 Elagolix blocks GnRH receptors in the pituitary gland, resulting in reduced production of luteinizing hormone and follicle stimulating hormone and a decrease in sex steroid secretion in the ovarian follicles, which leads to a reduction in the production and circulating concentration of estradiol. The FDA approved two doses of elagolix: 150 mg once daily for up to 24 months and 200 mg twice daily for up to 6 months. Importantly, elagolix at a dose of 150 mg once daily results in a mean circulating estradiol concentration of 41 pg/mL, indicating gentle suppression of ovarian estradiol production, and 200 mg twice daily results in a mean circulating ovarian estradiol concentration of 12 pg/mL, indicating strong suppression of ovarian estradiol production.3 For clinicians treating women with pelvic pain caused by endometriosis, these two elagolix regimens permit the individualization of hormonal therapy to the unique needs of each woman.